I. Technical Field
The present invention relates to a push-button switch cover member used for a push-button switching operation portion of a mobile computer such as cell-phone, personal digital assistant (PDA).
II. Related Art
In mobile computers, downsizing, especially reducing the thickness of key units has been desired so that a push-button switch cover member in which a number of keys (push buttons) used for switching operation are gathered in place and arranged on one keypad sheet made of rubber or elastomeric material. Such a push-button switch cover member can be assembled easily and leads to a decrease in the number of parts, so that the cover member having various functions and designs is now commonly used instead of a conventional mechanical switch.
In the push-button switch cover member, transparency or translucency is required in addition to the other functions such as electric insulation, heat resistance, low-temperature resistance, repetitive bondability, rebound resilience, because the cover member is backlit using a light source such as LED for improving operability of the mobile computer in a dark place, and that silicone rubber having excellent properties in such functions and transparency is now preferably used.
Furthermore, the mobile computer should have a good appearance and design to meet personal preference. Accordingly, in addition to these functions, a push-button switch cover member should have various designs on the keytop portion to cope with various preferences of users. However, silicone rubber has a poor chemical reactivity so that its surface should be treated by plasma treatment or priming with a coupling agent before applying a coating layer or adhering a keytop member made of another material onto its surface (For example, refer to Japanese Patent Publication No. H 7-296676 A and Japanese Patent Publication No. H 8-253607 A.